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Samenvatting - Human biology : concepts and current issues.

1.1 Life depends on water

Water molecules are polar.

Water is a liquid at body temperature.

Water can absorb and hold heat energy.

What is a solvent?

A solvent is a liquid in which other substances dissolve.

What is a solute?

A solute is any dissolved substance (opgeloste substantie).

Water keeps ions dissolved: water molecules are oriented around ions according to the principle that opposite charges attract.

What are hydropholic molecules?

Hydropholic molecules are polar molecules that are attracted to water and interact with it easily.

What are hydrophobic molecules?

Hydropholic molecules are nonpolar, neutral molecules (e.g. cooking oil) that don't interact easily with water and won't dissolve in it.

1.2 The importance of hydrogen ions

Bonds between hydrogen and oxygen in water are strong, but can break. When they do, the electron from one hydrogen atom is transferred to the oxygen atom completely, and the water molecule breaks into two ions: a hydrogen ion (H+) and a hydroxide ion (OH-).

What is an acid?

An acid is a molecule that can donate H+.

What is a base?

A base is a molecule that can accept H+.

pH scale = measure of the hydrogen io concentration of a solution, it ranges from 0-14.

Pure water: pH = 7 (neutral point).

Blood: pH = 7.4.

Acidic solution: pH less than 7. Higher h+ concentration than water.

Basic solution: pH greater than 7. Lower H+ concentration than water.

What is a mole?

A mole is a certain number of atoms, ions, or molecules.

What is a buffer?

A buffer is any substance that tends to minimize the changes in pH that might otherwise occur when an acid or base is added to a solution.

Pairs of related molecules that have opposite effects.

One of the pair is the acid form of the molecule (capable of donating H+) and the other is the base form (capable of accepting H+).

1.3 The organic molecules of living organisms

Organic molecules contain carbon and other elements held together by covlent bonds.

Carbon:

Ideal structural component (bouwsteen).

Has 6 electrons: 2 in the first shell (full) and 4 in the second (empty spaces).

Is most stable when its second shell is filled with 8 electrons.

Natural tendency is to form 4 covalent bonds with other molecules: H, N, O and C.

Dehydration synthesis: macromolecules are built within the cell itself.

Hydrolysis (reverse of dehydration synthesis): process where organic macromolecules are broken down. The equivalent of a water molecule is added each time a covalent bond between single subunits in the chain is broken. Releases energy.

4 classes of organic molecules:

Carbohydrates.

Lipids.

Proteins.

Nucleic acids.

1.4 Carbohydrates: used for energy and structural support

Monosaccharide = simplest kind of carbohydrate = sugar.

Most common ones contain 5 or 6 carbon atoms arranged in either a 5-membered or 6-membered rings.

The most important ones are ribose, deoxyribose, glucose and fructose.

Oligosaccharides = short strings (korte ketens) of monosaccharides linked together by dehydration synthesis.

Table sugar.

Sucrose (disaccharide) = glucose + fructose.

Lactose = glucose + galactose.

Maltose = glucose + glucose.

What are glycoproteins?

Glycoproteins are cell-membrane proteins that some oligosaccharides are covalently bonded to. They participate in linking adjacent cells together and in cell-cell recognition and communication

What are polysaccharides?

Polysaccharides are complex carbohydrates that form thousands of monosaccharides are joined together into straight or branced chains by dehydration synthesis. This is a convenient way for cells to stockpile extra energy by locking it in the bonds of the polysaccharide molecule.

The storage of polysaccharide is glycogen (starch in plants).

What is cellulose?

Cellulose is a form of glucose polysaccharide. We can't break down glucose units, but there's energy in it.